Communications systems and particularly communication systems involving wireless communication are built upon a shared medium that makes it easy for adversaries to launch denial of service (DoS) attacks. One form of a DoS attack is targeted at jamming a communication, or preventing sources from communicating. Jamming a communications system involves placing sufficient radio energy in the victim receiver to interfere with or totally obliterate the signal it is attempting to receive. These attacks can be easily accomplished by an adversary by either bypassing MAC-layer protocols, or emitting a radio signal targeted at jamming a particular channel.
Current art does not provide a jam-proof receiver. As a result, receivers must be designed to internally maximize the ratio of signal energy to jamming energy (S/J ratio). Many strategies are employed by wireless devices to evade a MAC/PHY-layer jamming-style denial of service attack. Conventional methods typically utilize classical techniques such as frequency hopping, direct sequence spread spectrum and other variations of digital processing to gain an advantage over a jammer trying to prevent or intercept a transmitted message. Frequency hopping anti-jam techniques generally involve hopping rapidly among many frequencies in an unpredictable sequence. No single frequency is used for a sufficient length of time to allow a jammer to scan the entire spectrum and locate the transmission. Spread spectrum anti-jamming techniques match transmitter, radio signal, and receiver characteristics, thereby preventing a party without a matching transmitter to jam the communication. Secondary modulation schemes may be utilized to spread the radio signal in time or bandwidth beyond that which is required by the information itself. Additionally, channel surfing, a form of spectral evasion that involves legitimate wireless devices changing the channel that they are operating on, may be utilized. Spatial retreats, whereby legitimate mobile devices move away from the locality of the DoS emitter, have also been employed to reduce jamming.
Disadvantageously, while these techniques may have predictable performance against a jammer, the techniques generally do not yield a workable solution when very powerful jammers are utilized and very low message error rates and high throughput are required by the network. Specifically, these techniques prevent adapting to dynamic network connectivity changes and result in less reliable message delivery. Such rigid routing on the basis of frequency or time may also lead to a limited number of high density traffic patterns. Concentrated relay transmissions can lead to easier platform detection by intercept receivers and subsequent jamming will lead to large disruptions of network communications. Also, the overloading of a platform's terminal resources with non-adaptive redundant routing leads to underutilization of network capacity and, hence, increased message delay and error. Specifically, a receiver must attempt to recover an original transmission from the fragments that have been sent redundantly on different frequencies or coded and spread across different frequencies, resulting in high message error rates. It is also desirable to reduce or avoid excessive redundant transmissions because they not only consume precious channel capacity, but result in increases in self-interference levels which, in turn, reduces anti-jamming protection.
Consequently, it would be advantageous if a method existed which provided improved jamming resistance for high throughput point to point communication networks.